The monitoring of CO2 concentration in both breath and the atmosphere plays an increasingly important role in research, environmental sensing, and personal healthcare [1-19]. The measurement of end-tidal CO2 (EtCO2, the level of carbon dioxide released at the end of expiration) can be used for the evaluation of systemic metabolism, perfusion and ventilation, which provides doctors and patients with a non-invasive and simple method to predict the presence and severity of asthma, Chronic Obstructive Pulmonary Disease (COPD), diabetic ketoacidosis, and a way to evaluate the effectiveness of treatment [8-12, 16-19]. Furthermore, the monitoring of CO2 level in the atmosphere is important for indoor air quality (IAQ) control as the indoor CO2 level is associated with increased prevalence of certain mucous membrane and lower respiratory sick building syndrome (SBS) symptoms [13-15].
Currently, most of the CO2 sensors in the market are based on infrared techniques [20, 21]. Such equipment is either costly and/or suffers from several drawbacks. For example, such devices are adversely affected by strong interference from humidity or require special pretreatment of the gas samples to reduce the humidity level, which limit their applications only in hospitals or in environments with controlled humidity levels. Thus, there is a need in the development of a small, low-cost, and easy-to-use CO2 sensor that anyone can use anytime and anywhere for a more complete and accurate assessment of a patient's disease status at home or, alternatively, in applications that allow better control of the indoor air quality.
The present disclosure provides a new and novel CO2 detector that can be used for the evaluation of respiratory therapy efficiency, prediction of diabetic ketoacidosis and monitoring of indoor air quality. The CO2 detector uses a new ultra-fast and reversible response pH-sensitive nanocomposite material on a microstructured hydrophobic substrate as a sensor element for CO2 detection, which changes color when exposed to CO2; and the concentration of CO2 is determined by measuring the change of light intensity on the sensor element. The CO2 sensor element disclosed herein for the first time has a long shelf life and can be used repeatedly. Also, when interfaced with appropriate hardware, the CO2 detector is capable of synchronizing with mobile devices, such as a cell phone or a tablet, acting as user interfaces so that the users can perform the test anytime and anywhere, and check the real-time data through a specific application.
Colorimetric-based CO2 sensors have been reported in literature [22-28] and also described in patents [29-36] and patent applications [37-41] ; however none of the previously reported sensors meet the features of time response, accuracy, specificity, and applicability to real samples as the one described in the present patent application.
U.S. Pat. Nos. 8,449,834; 6,709,403; 5,156,159; 4,994,117; 5,005,572 and 4,943,364 [29-34] disclose examples of CO2 detectors for semi-quantitative determination of CO2 levels in expired air. The CO2 detectors, which change colors in response to the presence of respiratory levels of CO2 (3.5-5%), are mostly used to monitor the placement of endotracheal tube and cannot provide accurate CO2 levels in breath.
U.S. Pat. Nos. 6,436,347 [35] and 7,578,971 [36] both describe the use of quaternary ammonium or quaternary phosphonium phase transfer agents with specific molecular structures to produce colorimetric CO2 detectors with fast and reversible response. Although these CO2 detectors may be capable to measure CO2 levels breath-by-breath, their response are not fast enough to monitor the breath CO2 patterns.
US. Patent Applications No. 2013/0259749 [37], and 2013/0150746 by us [41] disclose examples of CO2 detectors for CO2 analysis. While 2013/0259749 [37] emphasizes the configuration of CO2 detector, 2013/0150746 [41] emphasizes the used of the CO2 detector in conjunction with detection on O2. Both applications based their detection on a reactive (sensing) and a control (reference) signal to determine CO2 levels and O2 levels in breath. However, none of the publications emphasizes the importance of a combination of nanocomposite CO2 sensing materials on microstructured hydrophobic surfaces in conjunction with temperature, humidity and flow detection; which actually enables accurate CO2 quantification in, both, breath-by-breath and environment.